Electric power supply circuit

ABSTRACT

An electric power supply circuit includes a diode bridge circuit ( 12 ) for rectifying an alternating current, a switching element (S) for causing a short-circuit for output power of the diode bridge circuit ( 12 ), and a PAM control section ( 15 ) for causing the switching element (S) to perform switching with a predetermined timing so that a waveform of an input current approximates to a sine wave. The PAM control section ( 15 ) outputs ON/OFF pulses so that five pulses are output for each zero-cross point and one of the five pulses located in center extends over the zero-cross point at any time.

TECHNICAL FIELD

The present invention relates to an electric power supply circuit, andmore particularly, relates to a technique to improve controllability ofPAM control.

BACKGROUND ART

Conventionally, power supply apparatuses (power supply circuits) forconverting alternating current power to direct current power using arectifier circuit have been known. In a power supply apparatus of thistype, a high frequency current tends to be generated, resulting inreduction in power supply efficiency. To prevent such reduction in powersupply efficiency, for example, Patent Document 1 discloses a powersupply apparatus configured to reduce the high frequency current using aso-called PAM (pulse amplitude modulation) control.

Specifically, the power supply apparatus of Patent Document 1 includes arectifier circuit, which is a diode bridge circuit, and a smoothingcircuit. The smoothing circuit includes two capacitors coupled in serieswith each other, and a single capacitor coupled in parallel with the twocapacitors and is configured to perform double voltage rectificationbetween the smoothing circuit and the rectifier circuit. The powersupply apparatus further includes a switching element, provided at anoutput terminal of the rectifier circuit, for causing, when being turnedON, a short-circuit for output power of the rectifier circuit.

In the power supply apparatus, PAM control is performed. Specifically,in the rectifier circuit, the switching element is switched according tozero-cross points of an input voltage so that a waveform of an inputcurrent approximates to a waveform (a sine wave) of an input voltage.That is, an ON duty of a PAM waveform is controlled by this switchingoperation, so that the waveform of an input current approximates to asine wave. Accordingly, the high frequency current is reduced.

Patent Reference 1: Japanese Published Application No. 2001-145358DISCLOSURE OF THE INVENTION

Problems which the Invention is to Solve

According to Patent Document 1, the ON duty of a PAM waveform iscontrolled. Presumably, it is also possible to cause the waveform of theinput current to approximate to a sine wave by maintaining constantwidths of ON/OFF pulses of a PAM waveform and then controlling a phaseof the PAM waveform.

However, in such a case, as in Patent Document 1, when the power supplyapparatus is configured so that an ON pulse is output first at azero-cross point of an input voltage, the constant widths of ON/OFFpulses of the PAM waveform cannot be maintained. That is, when the phaseof the PAM waveform is shifted, and thus, for example, the ON pulse ofthe PAM waveform extends over the zero-cross point of the input voltage,an OFF pulse normally has to be output at the zero-cross point with anadvanced timing, compared to an output timing before the shift, toensure the constant width of ON pulses. However, in such a case, since apower supply apparatus is configured so that an ON pulse is outputfirst, an OFF pulse cannot be output with an adequate timing, and thus,the width of the ON pulse is increased.

As a possible solution to this problem, when the phase of the PAMwaveform is shifted, and thus, an ON pulse extends over the zero-crosspoint, an output order of ON and OFF pulses is changed so that an OFFpulse, instead of an ON pulse, is output first. Accordingly, however,two different output orders (output timings) of ON/OFF pulses have to beprovided, thus resulting in increase in complexity of control.

In view of the above-described points, the present invention has beendevised, and it is therefore an object of the present invention toprovide an electric power supply circuit, including a switching elementfor causing a short-circuit for output power of a rectifier circuit, forperforming PAM control, in which only one output timing of a PAMwaveform for ON/OFF pulses is provided and phase control of the PAMwaveform is performed.

Solution to the Problems

According to a first aspect of the present invention, an exampleelectric power supply circuit includes: a rectifier circuit (12),coupled to an alternating current power supply, for rectifying analternating current; a switching element (S) for causing, when beingturned ON, a short-circuit for output power of the rectifier circuit(12); and a PAM control section (15) for outputting, with apredetermined timing based on a zero-cross point of an input voltage ofthe rectifier circuit (12), a plurality of ON/OFF pulses to cause theswitching element (S) to perform switching so that a waveform of theinput current approximates to a sine wave. In this example power supplycircuit, the PAM control section (15) outputs the ON/OFF pulses so thatan ON pulse is generated to extend over the zero-cross point of theinput voltage of the rectifier circuit (12).

In the example electric power supply circuit, the PAM control section(15) outputs a PAM waveform including ON/OFF pulses with a predeterminedtiming based on a zero-cross point of an input voltage. Thus, theswitching element (S) performs switching with a predetermined timing, sothat the waveform of the input current is caused to be (to approximateto) a sine wave of the input voltage.

In the above-described PAM control, an ON pulse of the PAM waveform isoutput so as to extend over the zero-cross point of the input voltage atany time. Accordingly, in the PAM control, an output timing is set sothat an OFF pulse is output first at a predetermined time point after alapse of a certain time from the zero-cross point, and subsequently, anON pulse is output. In this case, even when the phase of the PAMwaveform is shifted due to some disturbance or the like, the ON pulseextending over the zero-cross point before the shift still staysextending over the zero-cross point. Thus, an OFF pulse is output firstwith a predetermined timing base on the zero-cross point.

According to a second aspect of the present invention, in the exampleelectric power supply circuit of the first aspect, the PAM controlsection (15) is configured so that an ON/OFF pulse group formed of theON pulse extending over the zero-cross point, and one or more ON pulsesgenerated both before and after the ON pulse and having a smaller widththan that of the ON pulse is generated for each zero-cross point.

In this example electric power supply circuit, the ON/OFF pulse group isgenerated for each zero-cross point. Thus, the waveform of the inputcurrent is caused to be a smoother sine wave. Moreover, the ON pulseextending over the zero-cross point has a larger width than the width(s)of the one or more ON pulses generated both before and after the ONpulse, so that, even though the phase of the PAM waveform is shifted, itis possible to reliably maintain a state where the ON pulse extends overthe zero-cross point P.

According to a third aspect of the present invention, in the exampleelectric power supply circuit of the first or second aspect, the PAMcontrol section (15) includes a zero-cross detector section (5 a) fordetecting an increase in the input voltage of the rectifier circuit (12)toward the zero-cross point to a level equal to or higher than apredetermined level, a timer section (5 c) for resetting and starting acount each time the zero-cross detector section (5 a) detects theincrease in the input voltage; and a PAM waveform output section (5 b)configured to output with a predetermined timing, using a count of thetimer section (5 c), an OFF pulse first after a lapse of a certain timefrom a first zero-cross point since the detection by the zero-crossdetector section (5 a), and thereafter, alternately output ON and OFFpulses with a predetermined timing.

In this example electric power supply circuit, the zero-cross detectorsection (5 a) detects a certain point at which the input voltage risestoward the zero-cross point. That is, a point prior to the zero-crosspoint is detected only once in one cycle of the input voltage. When theprior point to the zero-cross point is detected, the timer section (5 c)starts a count. Also, when the zero-cross detector section (5 a) detectsthe prior point, an OFF s pulse is output first from the PAM waveformoutput section (5 b) at a predetermined count of the timer section (5c). Thereafter, ON and OFF pulses are alternately output with apredetermined timing. Thus, a desired PAM waveform is generated. Thatis, in consideration of an amount of time between detection by thezero-cross detector section (5 a) and a first zero-cross point, thepredetermined timing with which OFF/ON pulses are output so that an OFFpulse is output first and an ON pulse is subsequently output is set inthe PAM waveform output section (5 b).

According to a fourth aspect of the present invention, in the exampleelectric power supply circuit of the third aspect, when an output phaseof ON/OFF pulses is shifted, the PAM waveform output section (5 b) isconfigured to correct an output timing of each of the ON/OFF pulses byan amount corresponding to a shift each time the zero-cross detectorsection (5 a) detects the increase in the input voltage.

In this example electric power supply circuit, when the phase of ON/OFFpulses is shifted, the output timing in the PAM waveform output section(5 b) is corrected accordingly. For example, in FIG. 2, when the phaseof the waveform is shifted to the left, the output timing is correctedto be advanced and, in contrast, when the phase of ON/OFF pulses isshifted to the right, the output timing is corrected to be delayed. Atthe time of the correction, an ON pulse extending over the zero-crosspoint before the phase is shifted still stays extending over thezero-cross point.

According to a fifth aspect of the present invention, in the exampleelectric power supply circuit of the second aspect, the ON/OFF pulsegroup is formed of ON/OFF pulses arranged in a symmetrical pattern withrespect to the ON pulse extending over the zero-cross point.

In this example electric power supply circuit, the number of ON/OFFpulses included in the ON/OFF pulse group is an odd number. That is, thesame number of pulses are generated before and after the ON pulseextending over the zero-cross point so that each pulse located beforethe zero-cross point has the same width as an associated one of pulseslocated after the zero-cross point.

According to a sixth aspect of the present invention, in the exampleelectric power supply circuit of any one of the first through thirdaspects, the rectifier circuit is a diode bridge circuit (12), and theelectric power supply circuit is configured so that two capacitors (C1and C2) coupled in series with each other are provided at an output sideof the diode bridge circuit (12), an input side of the diode bridgecircuit (12) and a point between the two capacitors (C1 and C2) arecoupled via the switching element (S), and thereby, double voltagerectification is performed.

In this example electric power supply circuit, for example, as shown inFIG. 1, a circuit for performing double voltage rectification isachieved. That is, the example electric power supply circuit of thepresent invention is configured so as to be switched to serve as adouble voltage rectifier circuit when the switching element (S) isturned ON, and to be switched to serve as a full-wave rectifier circuitwhen the switching element (S) is turned OFF.

Effects of the Invention

According to the present invention, ON/OFF pulses are output so that anON pulse is generated to extend over a zero-cross point of an inputvoltage of the rectifier circuit (12). Thus, even when a phase of awaveform (PAM waveform) including the ON/OFF pulses is shifted, an OFFpulse is output first at any time. That is, it is sufficient to set onlyone output timing with which an OFF pulse is output first. Accordingly,a plurality of output timings do not have to be prepared, so that PAMcontrol can be simplified.

Furthermore, ON/OFF pulses can be reliably output with a predeterminedtiming. Thus, a desired PAM waveform can be reliably generated. As aresult, the waveform of an input current can be reliably caused to be asine wave, so that the high frequency current can be further reduced.

According to the third aspect of the present invention, ON/OFF pulsesare output with a predetermined timing using a count of the timersection (5 c). Thus, as described above, only one output timing has tobe provided, so that it is not necessary to prepare multiple timings forthe timer section (5 c). Thus, in contrast to the known technique inwhich, when the ON pulse no longer extends over the zero-cross point P,another timer section for starting a count with another timing isadditionally needed, there is no need to provide an additional timersection. Therefore, the configuration of the microcomputer (15) can besimplified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic wiring diagram illustrating a configuration of anentire electric power supply circuit according to an embodiment of thepresent invention.

FIG. 2 is a waveform diagram showing the relationship between an inputvoltage and a zero-cross signal.

FIG. 3 is a waveform diagram showing an output state of a PAM waveform.

FIG. 4 is a waveform diagram describing an output timing of the PAMwaveform.

FIG. 5 is a waveform diagram showing an output state of the PAM waveformwhen a phase of the PAM waveform is shifted.

FIG. 6 is a waveform diagram describing an output timing of the PAMwaveform when the phase of the PAM waveform is shifted.

EXPLANATION OF REFERENCE NUMERALS

10 Electric power supply circuit

12 Diode bridge circuit (rectifier circuit)

15 Microcomputer (PAM controller section)

5 a Zero-cross detector section

5 b PAM waveform output section

5 c Timer section

S Switching element

D1 through D4 Diode

C1, C2 Capacitor

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

As shown in FIG. 1, an electric power supply circuit (10) according tothis embodiment includes a converter circuit (11), an inverter circuit(14) and a microcomputer (15).

The electric power supply circuit (10) is configured to rectifyalternating current power in the converter circuit (11), convert therectified direct current to a three-phase alternating current in theinverter circuit (14), and supply the three-phase alternating current toan electric motor drive (30). The electric motor drive (30) drives acompressor provided in a refrigerant circuit in an air conditioningsystem. Although not shown in FIG. 1, the refrigerant circuit of the airconditioning system is configured so that the compressor, a condenser,an expansion mechanism and an evaporator are coupled to form a closedcircuit. Thus, a refrigerant circulates in the closed circuit, therebyperforming vapor compression refrigeration cycle. In a coolingoperation, air cooled by the evaporator is supplied into a room. In aheating operation, air heated by the condenser is supplied into a room.

The converter circuit (11) is coupled to an alternating current powersupply (20) to rectify alternating current power. The converter circuit(11) includes a reactor (L) as well as a diode bridge circuit (12) and asmoothing circuit (13).

The diode bridge circuit (12) is coupled to the alternating currentpower supply (20) and including bridge-connected four diodes (D1 throughD4). That is, the diode bridge circuit (12) rectifies alternatingcurrent power and serves as a rectifier circuit according to the presentinvention.

The smoothing circuit (13) is provided at an output side of the diodebridge circuit (12). The smoothing circuit (13) includes two capacitors(C1 and C2) coupled in series with each other, and a capacitor (C3)coupled in parallel to the two capacitors (C1 and C2). The twocapacitors (C1 and C2) coupled in series with each othercharge/discharge an output voltage of the diode bridge circuit (12). Thecapacitor (C3) coupled in parallel to the capacitors C1 and C2 smoothesan output voltage (V₀) of the two capacitors (C1 and C2). That is, thesmoothing circuit (13) double-voltage rectifies a voltage between thesmoothing circuit (13) and the diode bridge circuit (12).

The reactor (L) is coupled between one of electrodes of the alternatingcurrent power supply (20) and the diode bridge circuit (12).

The converter circuit (11) includes a switching element (S) capable ofswitching bidirectionally between ON and OFF. The switching element (S)is coupled between an input side of the diode bridge circuit (12) and apoint between the two capacitors coupled in series with each other. Thatis, the converter circuit (11) of this embodiment is turned to serve asa double voltage rectifier circuit when the switching element (S) isswitched ON, and is turned to serve as a full-wave rectifier circuitwhen the switching element (S) is turned OFF.

The inverter circuit (14) converts a direct current voltage of thecapacitor (C3) to a three-phase alternating current voltage, andsupplies the three-phase alternating current voltage to the electricmotor drive (30). Note that, although not shown, the inverter circuit(14) has a general configuration in which, for example, six switchingelements are coupled with one another in the form of a three-phasebridge.

The microcomputer (15) performs, in addition to switching control of theinverter circuit (14), PAM (pulse amplitude modulation) control of theconverter circuit (11), and serves as a PAM control section according tothe present invention. The microcomputer (15) includes a zero-crossdetector section (5 a), a PAM waveform output section (5 b) and a timersection (5 c).

The electric power supply circuit (10) of this embodiment furtherincludes a voltage detector circuit (16) for detecting an input voltage(Vi) of the diode bridge circuit (12), and a current detector circuit(17) for detecting an input current (IL).

As shown in FIG. 2, the zero-cross detector section (5 a) outputs azero-cross signal (ON/OFF signal) according to the input voltage (Vi)detected by the voltage detector circuit (16). Specifically, thezero-cross detector section (5 a) outputs an ON signal if the inputvoltage (Vi) is lower than a predetermined level, and is turned OFF ifthe input voltage (Vi) is equal to or higher than the predeterminedlevel. That is, by detecting a trailing edge point of the ON signal(hereinafter merely referred to as a “trailing edge point”), it isdetected that the input voltage (Vi) has been increased toward azero-cross point P to be equal to or higher than the predetermined level(see FIG. 3). Accordingly, there is a certain time lag (tzwav) betweenthe trailing edge point and the zero-cross point P.

As shown in FIG. 3, when a trailing edge point is detected by thezero-cross detector section (5 a), the timer section (5 c) starts acount. When a subsequent trailing edge point is detected by thezero-cross detector section (5 a), the timer section (5 c) is reset andstarts a new count. In this manner, the timer section (5 c) is reset andstarts a new count each time the zero-cross detector section (5 a)detects a trailing edge point.

As shown in FIG. 3, the PAM waveform output section (5 b) outputs ON/OFFpulses (PAM waveform) which are pulse signals for causing the switchingelement (S) to perform switching. The PAM waveform output section (5 b)outputs ON/OFF pulses so that the waveform of the input current (IL) iscaused to be similar (to approximate) to a sine waveform of the inputvoltage (Vi). Specifically, the PAM waveform output section (5 b)outputs, using a count by the timer section (5 c), ON/OFF pulses with apredetermined timing (output timing) each time a trailing edge point isdetected by the zero-cross detector section (5 a). That is, ON/OFFpulses are output with a predetermined timing based on the zero-crosspoint P of an input voltage (i.e., a first zero-cross point after atrailing edge point detected by the zero-cross detector section (5 a)).

As shown in FIG. 3, the PAM waveform output section (5 b) outputs ON/OFFpulses so that a pulse group consisting of five pulses is generated foreach zero-cross point. The pulse group is generated so that a centerpulse 1 (ON pulse) has a larger width than widths of the other fourpulses 2 through 5, and has a symmetrical pattern with respect to thecenter pulse 1. In the pulse group, as shown in FIG. 3, dimensions tw1through tw5 are fixed. That is, according to this embodiment, a pulsewidth of the pulse group is fixed.

The PAM waveform output section (5 b) outputs ON/OFF pulses so that thecenter pulse 1 is generated to extend over the zero-cross point P at anytime. An output timing for ON/OFF pulses is set so that, when a trailingedge point is detected, the PAM waveform output section (5 b) outputs anOFF pulse first, and thereafter, alternately outputs ON and OFF pulses.Thus, according to this embodiment, so-called multi-pulse control inwhich a plurality of pulses (ON pulses) are generated in half cycle ofthe input voltage (Vi) is performed.

The PAM waveform output section (5 b) is configured to correct, when aphase of the PAM waveform is shifted, the output timing so that theoutput timing is shifted by an amount corresponding to the phase shift.Specifically, in FIG. 2, when the phase of the PAM waveform is shiftedto the right, the output timing is corrected to be delayed by the amountcorresponding to the phase shift and, when the phase of the waveform isshifted to the left, the output timing is corrected to be advanced bythe amount corresponding to the phase shift.

Next, a specific PAM waveform output operation will be described indetail with reference to FIG. 3 through FIG. 6.

As shown in FIG. 3, when a trailing edge point of a zero-cross signal isdetected by the zero-cross detector section (5 a), the timer section (5c) starts a count. Then, the PAM waveform output section (5 b) outputsON/OFF pulses with a predetermined timing. Specifically, as shown inFIG. 4, when a count of the timer section (5 c) is “t1,” an OFF pulse isoutput first. Subsequently, each time the count of the timer section (5c) becomes “t2”, “t3”, . . . “t18” or ‘t19,” an ON/OFF pulse is outputso that ON and OFF pulses alternately appear. Thus, the PAM waveformcorresponding to one cycle of an input voltage is output. Inconsideration of a (estimated) time between the trailing edge point andthe zero-cross point P, the count values “t2,” “t3,” . . . “t18” and“t19” are given so that a PAM waveform is output with a predeterminedtiming based on the zero-cross point P.

When a subsequent trailing edge point of the zero-cross signal isdetected, the timer section (5 c) is reset and restarts a count. Thus,ON and OFF pulses are alternately output with the same timing as theoutput timing described above. In this case, since each ON pulse isgenerated so as to extend over the zero-cross point P, an OFF pulse isoutput first as desired. Therefore, a desired PAM waveform can bereliably generated.

In this embodiment, when the waveform of an input current is distorteddue to distortion of an input voltage or the like, a control in whichthe phase of the PAM waveform is shifted to cause the waveform of theinput current to approximate to a sine wave. Hereinafter, the case wherethe phase of the PAM waveform is shifted to the right as viewed in FIG.2 will be described.

As shown in FIG. 5, when the PAM waveform is shifted to the right by Δt,the output timing set in the PAM waveform output section (5 b) iscorrected. That is, the output timing set at an initial stage iscorrected to be delayed by Δt. Thus, when a trailing edge point of azero-cross signal is detected and the timer section (5 c) starts acount, the PAM waveform output section (5 b) outputs ON/OFF pulses withthe corrected timing.

Specifically, as shown in FIG. 6, first, when a count of the timersection (5 c) becomes “t1+Δt,” an OFF pulse is output. Subsequently,each time the count of the timer section (5 c) becomes “t2+Δt,” “t3+Δt,”. . . “t18+Δt” or “t19+Δt,” an ON/OFF pulse is output so that ON and OFFpulses alternately appear. Thus, a PAM waveform can be generated withoutchanging the pulse width of the pulse group and predetermined dimensionsof tw1 through tw5.

Moreover, even when the phase of the PAM waveform is shifted, the pulse1 (ON pulse) can be maintained to extend over the zero-cross point P.Thus, each time a trailing edge point is detected, an OFF pulse isreliably output. Accordingly, a desired PAM waveform can be reliablygenerated.

Note that, in contrast to the above, in the case where the phase of thePAM waveform is shifted by Δt to the left as viewed in FIG. 2, when thecount of the timer section (5 c) becomes “t1−Δt,” an OFF pulse isoutput. Subsequently, each time the count becomes “t2−Δt,” “t3−Δt,” . .. “t18−Δt” or “t19−Δt,” an ON/OFF pulse is output so that ON and OFFpulses alternately appear. In this case, a PAM waveform can be generatedwithout changing the pulse width of the pulse group and thepredetermined dimensions of tw1 through tw5.

Effects of First Embodiment

According to this embodiment, ON/OFF pulses are output so that an ONpulse of the pulse group is generated to extend over the zero-crosspoint P of an input voltage. Thus, even though a phase of a PAM waveformis shifted, an OFF pulse can be output first at any time. Specifically,according to a known technique, when the phase of the PAM waveform isshifted, so that an ON pulse no longer extends over the zero-cross pointP and, instead, a subsequent OFF pulse extends over the zero-cross pointP, an ON pulse has to be output first. Accordingly, two differenttimings, i.e., an output timing with which an ON pulse is output first,and another output timing with which an OFF pulse is output first areneeded. However, according to this embodiment, in contrast to the knowntechnique, only one output timing is needed. Accordingly, a plurality ofoutput timings do not have to be prepared, so that PAM control can besimplified and also improved controllability for the PAM control can beachieved.

Moreover, since only one output timing is needed, it is not necessary toprepare multiple timings for the timer section (5 c). That is, asituation where, in addition to the timer section (5 c) of thisembodiment, another timer section for starting a count for anothertiming has to be provided when an ON pulse does not extend over thezero-cross point P can be avoided. Accordingly, the configuration of themicrocomputer (15) can be simplified.

As described above, ON/OFF pulses can be output with a predeterminedtiming. Thus, a desired PAM waveform can be reliably generated. As aresult, the waveform of the input current can be reliably caused to be asine wave, so that the high frequency current can be further reduced.

In the pulse group, a pulse (pulse 1) extending over the zero-crosspoint P is generated to have a larger width than the widths of the otherpulses, so that it is possible to maintain a state where the pulse 1extends over the zero-cross point P. Thus, a predetermine PAM controlcan be reliably performed.

Moreover, according to this embodiment, the pulse group is generated foreach zero-cross point. Thus, a waveform of an input current can becaused to be a smoother sine wave.

Other Embodiments

The electric power supply circuit of the above-described embodiment mayhave the following configuration.

For example, according to the above-described embodiment, the pulsegroup to be generated for each zero-cross point includes five pulses.However, the number of pulses included in the pulse group is not limitedthereto, but may be seven or nine. Also, the number of the pulses in thepulse group is not limited to an odd number, but may be an even number.

According to the above-described embodiment, the timer section (5 c)starts a count at a trailing edge point of the zero-cross signal.However, the present invention is not limited thereto. For example, thezero-cross detector section (5 a) may be configured to detect thezero-cross point P itself, and then, the timer section (5 c) may beconfigured to start a count at the zero-cross point P.

The above-described embodiment is merely illustrative of the presentinvention, and there is no intention to limit the scope of thedisclosure, products to which the disclosure is applied and itsapplication.

INDUSTRIAL APPLICABILITY

As has been described, the present invention is useful as an electricpower supply circuit for reducing a high frequency current in arectifier circuit by performing a PAM control.

1. An electric power supply circuit comprising: a rectifier circuit(12), coupled to an alternating current power supply, for rectifying analternating current; a switching element (S) for causing, when beingturned ON, a short-circuit for output power of the rectifier circuit(12); and a PAM control section (15) for outputting, with apredetermined timing based on a zero-cross point of an input voltage ofthe rectifier circuit (12), a plurality of ON/OFF pulses to cause theswitching element (S) to perform switching so that a waveform of theinput current approximates to a sine wave, wherein the PAM controlsection (15) outputs the ON/OFF pulses so that an ON pulse is generatedto extend over the zero-cross point of the input voltage of therectifier circuit (12).
 2. The electric power supply circuit of claim 1,wherein the PAM control section (15) is configured so that an ON/OFFpulse group formed of the ON pulse extending over the zero-cross point,and one or more ON pulses generated both before and after the ON pulseand having a smaller width than that of the ON pulse is generated foreach zero-cross point.
 3. The electric power supply circuit of claim 1or 2, wherein the PAM control section (15) includes a zero-crossdetector section (5 a) for detecting an increase in the input voltage ofthe rectifier circuit (12) toward the zero-cross point to a level equalto or higher than a predetermined level, a timer section (5 c) forresetting and starting a count each time the zero-cross detector section(5 a) detects the increase in the input voltage; and a PAM waveformoutput section (5 b) configured to output with a predetermined timing,using a count of the timer section (5 c), an OFF pulse first after alapse of a certain time from a first zero-cross point since thedetection by the zero-cross detector section (5 a), and thereafter,alternately output ON and OFF pulses with a predetermined timing.
 4. Theelectric power supply circuit of claim 3, wherein, when an output phaseof ON/OFF pulses is shifted, the PAM waveform output section (5 b) isconfigured to correct an output timing of each of the ON/OFF pulses byan amount corresponding to a shift each time the zero-cross detectorsection (5 a) detects the increase in the input voltage.
 5. The electricpower supply circuit of claim 2, wherein the ON/OFF pulse group isformed of ON/OFF pulses arranged in a symmetrical pattern with respectto the ON pulse extending over the zero-cross point.
 6. The electricpower supply circuit of claim 1 or 2, wherein the rectifier circuit is adiode bridge circuit (12), and the electric power supply circuit isconfigured so that two capacitors (C1 and C2) coupled in series witheach other are provided at an output side of the diode bridge circuit(12), an input side of the diode bridge circuit (12) and a point betweenthe two capacitors (C1 and C2) are coupled via the switching element(S), and thereby, double voltage rectification is performed.